A known fuel delivery pipe having a fuel path is one of fuel system parts for internal combustion. A surface on the fuel path is plated with nickel-phosphorus, etc. In general, nickel-phosphorus plating is used for protecting a wall surface defining a fuel path against corrosion by alcohol-mixed fuel such as biofuel. On the other hand, the outer surface of the fuel delivery pipe is rust proofed as a countermeasure against salt corrosion. A known method of manufacturing such a fuel delivery pipe will hereinafter be illustrated with reference to FIGS. 8 through 10.
First, a crude metal 1 is cut out from a forged iron rod (a forging cutting step). Second, the crude metal 1 is drilled through its axis such that a round bore 2 is formed inside the crude metal 1 (a machining step). Third, the crude metal 1 with the round bore 2 is impregnated in nickel-phosphorus plating solution and is electroless plated. By this plating, a nickel-phosphorus plating layer 3 is formed both on an inner periphery of the round bore 2 and on the outer periphery of the crude metal 1 (a nickel-phosphorus plating step). Fourth, rubber plugs 4 are fitted tightly into opening ends of the crude metal 1 to prevent paint from entering the inside of the crude metal 1. That is, the inside of the crude metal 1 is masked (a masking step). Finally, the outer periphery of the crude metal 1 is coated with a paint film 5 (an outer-periphery coating step). Thus, a fuel delivery pipe 6 having the nickel-phosphorus plating layer 3 on the inner periphery of the crude metal 1 and the paint film 5 on the outer periphery of the crude metal 1 is manufactured.
As illustrated in FIG. 10, the fuel delivery pipe 6 has four layers including the nickel-phosphorus plating layer 3, the crude metal 1, the nickel-phosphorus plating layer 3, and the paint film 5, in that order from the fuel path 7. That is, two nickel-phosphorus plating layers 3 are necessarily formed on the fuel delivery pipe 6. However, the nickel-phosphorus layer plating 3 on the periphery that does not contact fuel is needless. Therefore, while nickel is one of rare metals, a larger quantity of nickel is required. Furthermore, the fuel path 7 needs to be sealed with the rubber plugs 4 before the outer periphery is coated with the paint film 5. That is, an extra step (the masking step) is needed prior to the outer-surface coating step. Therefore, reduction in use of nickel and, further, avoiding the masking step are important problems for reducing the cost of manufacturing the fuel delivery pipe 6.
Thus, there is a need for a fuel delivery pipe that needs less nickel and does not need the masking step, thereby reducing the manufacturing cost.